1. Field of the invention
This invention relates to an optical recording medium and a process for production thereof.
2. Related Background Art
In recent years, information recording has progressed. Many optical recording media and information recording and/or reproducing apparatuses which record and/or reproduce information optically such as optical discs, optical cards, optical tapes and so on have been proposed. Desirable features of the optical information recording media (hereafter referred to as optical recording media) are high recording density, long lifetime, and a large capacity compared to their size arise because the media can be recorded on and reproduced from without being contacted.
Some portable optical recording media such as optical card type media have been proposed, researched and developed recently. Amongst such media, there is a proposal that visible information, for example character information or picture information such as the distributor's name for the media, the system title, the owner's name and so on is added.
In the past, such added information on the optical recording medium was generally executed on a region other than the region (hereinafter referred to as optical recording region) where the optical recording layer of the optical recording medium was provided.
FIGS. 1 to 6 illustrate prior art recording media, equivalent features in FIGS. 1 to 4 being denoted by corresponding reference numerals.
FIGS. 1 and 2 illustrate an optical recording media including visible information as described in Japanese laid open patent JP-A-64-16696. In FIGS. 1 and 2, FIGS. 1(a) and 2(a) are plan views of an optical card, whilst FIGS. 1(b) and 2(b) are respectively, cross-sections along the lines A--A, and B--B of FIGS. 1(a) and 2(a).
The optical recording media shown in these figures comprise a hard coat layer 101 and a transparent substrate 102 having a preformat pattern 103 comprising prepits and pregrooves. An optical information recording portion 104 is formed on a surface of the substrate having the preformat pattern 103. The card also includes an adhesive layer 105, back substrate 106, and a printed layer 107 including a portion carrying visible information 108.
In the medium shown in FIG. 1, the printed layer 107 including the visible information 108 is formed on the outside surface of the back substrate 106. In the medium shown in FIG. 2, the printed layer 107 is formed on the adhesive layer 105 side of the back substrate 106. In this particular structure, the region for carrying character information or picture information is restricted. Furthermore, there is the problem that this arrangement restricts the design of the optical recording medium. The addition of an IC chip, magnetic stripes, or a photograph of a human face on the optical card was investigated in order to produce an ID card or a machine readable card representing money. In these cases the region on which the visible information can be added becomes very narrow.
FIG. 3a illustrates a plan view and FIG. 3b illustrates a cross-sectional view along the line C--C of the recording medium shown in JP-A-2-30595 of FIG. 3.
In this optical recording medium, an optical recording layer 104 composed of polymethine dye was formed so as to cover the visible information portion which is formed on the back substrate 106. It is then possible to read out the visible information 108 through the recording layer 104.
FIG. 4 illustrates an optical recording medium as disclosed in JP-A-2-247820. FIG. 4(a) is a plan view of the medium, FIG. 4(b) is an enlarged plan view of the optical recording portion of the medium, and FIG. 4(c) is a cross sectional view along line D--D of FIG. 4(a).
In this medium, the visible information portion 108 is formed on the surface of an optical recording medium substrate 411. The optical recording portion 104 is formed on the surface of the visible information portion 108, the surface also carrying a magnetic stripe 401. In this structure it is possible to read out the visible information 108 through the optical recording portion 104.
JP-A-6-176519 discloses two optical cards which are capable of having added enough general information by reading out information stored under the optical recording layer. The structure of these optical cards are explained referring to FIGS. 5 and 6 in which FIGS. 5a and 5b show, respectively, a plan view and cross sectional side view along the line E--E of the first card, and FIG. 6 shows a side view of the second card, the plan view being the same as the first card.
In FIG. 5 the optical card 501 is formed as follows. A surface side printed layer 503, an adhesive layer 504, optical recording medium 505, transparent protective layer 506 are laminated in this order on a card base 507. On the underside of the card base 507, a back side printed layer 508 is formed. The back side printed layer 508 is covered with a transparent back side printed protective layer 509. On the surface side printed layer 503, two sets of barcodes 511A,B including card information indicative of an attribute of the card is formed. The barcodes 511A,B are laminated under the optical recording medium 505. As a transparent medium is used as the optical recording medium 505, the barcodes 511A,B can be read out through the transparent protective layer 506 and optical recording medium 505.
Turning now to FIG. 6, the optical card 501 is formed as follows. The adhesive layer 504, optical recording medium 505, transparent protective layer 506 are formed on a transparent card base 513. On the underside of the card base 513 is a surface side printed layer 503, a back side printed layer 508 and a back side printed protective layer 509 are formed. The barcodes 511A,B are formed on the surface side printed layer 503 so as to be read out through the transparent protective layer 506, the optical recording medium 505, the adhesive layer 504 and the transparent card base 513.
However, all prior art described above is devoid of any disclosure about an optical recording medium capable of including high contrast visible information having no influence on the recording and reproducing characteristics of the optical recording medium.